Refreshed crt display with ecg

ABSTRACT

A monitor for the display of electrocardiogram (ECG) signals. The signals from the patient are digitized and enter a main memory. The data is recycled and continually updated. The data is displayed as real time on a cathode ray tube (CRT) in such a manner that the data originally entered moves from right to left across the scope in the same position. Thus, at approximately five seconds the data is at the left of the screen. All subsequent data follows the same pattern whereby the display on the CRT appears as a continuously moving waveform. An alarm memory receives data five seconds old and stores the data for five seconds. If the ECG signals from the patient violate certain limits, an alarm is actuated. The data in the alarm memory at the time of the alarm is sealed off and displayed as a stationary waveform on the CRT with the real time display.

MiG-870A United States Zambuto 1 Feb. 19, 1974 1 1 REFRESHED CRT DISPLAY WITH ECG Primary ExaminerPaul J. Henon [76] Inventor: Raymond Peter Zambuto 354 Asszslant Examme lohn P. Vandenburg pp Rd Tewksbury, Mass Attorney, Agent, or Firm-Richard L. Stevens (H876 I57] ABQTRACT hcd: Sept 1971 A monitor for the dis In of clcctrocardio ram (ECG) P y t,

[21] Appl. No.: 185,322 signals. The signals from the patient are digitized and enter a main memory. The data is recycled and continually updated. The data is displayed as real time on [52] U.S. Cl 340/172.5, 340/324 A, 128/206 a cathode y tube (CRT) in Such a manner that the [51] Int. Cl G061 3/14, G06f 15/42 [58] Field of Search 340/172 5 324 235/197 data originally entered moves from right to left across h 128/2 the scope in the same position. Thus, at approximately five seconds the data is at the left of the screen. All

'[ References Cited subsequent data follows the same pattern whereby the display on the CRT appears as a continuously moving UNITED STATES PATENTS waveform. An alarm memory receives data five sec- 3,652,999 3/1972 Hjort 340/1725 nds 01d and stores the data for five seconds. If the 3,333,247 7/1967 Hadley 340/172-5 ECG signals from the patient violate certain limits, an

r in 54 73 t g im is actuated. The data in the alarm memory at e tini o f the alarm is sealed off and displayed as a 3,566,365 2/1971 Rawson 340/1725 Stationary waveform on the CRT with the real time display.

33 Claims, 14 Drawing Figures 32m AMPLIFIER o zoo QZE 230 CRT HT a AVF (omen/10m (H6 9) (RG15) s? t co iir ot (F16 31 7 4 PATIENT gg f ALARM ISOLATOR 5 SEC (FIG. 8) MEMORY (FIG. 12) 555515 1) DEIQSCSTOR FLASHER SR EE We 4) LQtSYSTOLt-Z) el m4 G3 1 I TACHOMETER- ZAIEZ 84 (FIG 5) AUDIO (VISUAL) BRADY CARDIA UMP: at? FOR 0 DELAY E? (FIG- 1i r 5 SEC new I I a ,4

PATENTEUFEBIQIQM 3.793.626

' saw 1n 0? 14 REFRESHED CRT DISPLAY WITH ECG BACKGROUND OF THE INVENTION The cathode ray tube was commercially introduced into medical monitoring in the nineteen fiftys. The display produced consisted in writing the electrocardiogram across the screen of the tube. In this type of display a narrow beam of electrons is directed onto a phosphor coated screen. Electrons striking the screen at a particular location cause the phosphor at that location to glow. Diversion of the electron beam from that location will cause the glowing phosphor to fade out. Thus in the conventional display a bright spot is seen to move across the screen at 25 mm/sec. moving vertically in direct proportion to the electrical signals from the patients heart. This type of display has remained essentially unchanged. It suffers from the fact that while the phosphor does continue to glow slightly after the electron beam passes over it, in the ambient light levels of todays hospitals, the display is far from optimal in terms of readability and recognition of arrythmias.

Recently, a new type of display has appeared. This is the infinite persistence type display. Within this type of display, the electrocardiogram signal information is preserved at full brilliance on the screen for some predetermined amount of time (usually l to seconds), giving the operator a clear view of arrythmias. A number of approaches have been made in this area. Among these have been (a) direct display of the data on a commercial storage cathode ray tube, (b) temporary storage of the data on a delay line and display on a television raster system, and (c) digitization of the data, temporary storage in a central computer, and conventional sweep display. Each of the above systems suffers from very definite drawbacks. Display of the data on a storage CRT suffers from two shortcomings in that the life of the storage tube itself is limited as compared with conventional CRTs, and the data itself is printed across the screen. This means that information appearing on the right side of the screen is erased as soon as it appears, and only information presented on the left side of the screen remains in view long enough for verification of possible arrythmias. These defects are eliminated by the raster display system. In this method the signal is passed through an acoustic delay line and stored there temporarily. As new data is fed into the line, old data (4-8 seconds) is removed. Thus the most recent history of the patients ECG is retained. This memory is continually scanned and presented on a vertical raster display. This type of display uses a standard long-life CRT. The data itself is pulled" across the screen. New data appears on the right side of the screen and moves slowly leftward across the screen, disappearing at the left edge of the screen. Thus, a given ECG complex remains visible on the screen for several seconds after occurrence.

The raster display system currently available also has certain disadvantages. The display itself is composed of a series of dots and has a discontinuity which is particularly noticeable in the QRS complex. The only available system is in the form of a central Nurses station display. This system accepts conventional signals from bedside monitors, creates the nonfading display, and

the persistent display may appear also at the bedside.

This central processor concept allows for no failure margin. If the central delay line undergoes a major failure, the entire display system for up to four patients is affected.

The conventional swept display takes the data from the patient, converts it to a series of digital signals and stores it in a central computer. Like the raster display the data in memory is continually updated, and the data is pulled" across the screen from right to left. Unlike the raster display, however, the data appears more continuous than segmented. The unit itself is once again central and a failure can affect up to eight patient displays both at the bedside and the Nurses station, leaving the medical staff with no analog waveform display.

SUMMARY OF THE INVENTION My invention embodies an apparatus and method for the storing of signals and eventual waveform display of the signals. The signals preferably are stored in at least two conditions, real time, and delay or alarm time. The real time signals are displayed in analog form on a recording medium. A waveform corresponding to the real time signal is analyzed to determine if it violates a preset condition or predetermined limits. If the limits are violated, then the stored alarm signals may then be displayed on the same or a different recording medium. Both the real time and alarm signals may be displayed on the same cathode ray tube, two different cathode ray tubes, on a cathode ray tube and an analog pen recorder, on two analog write-out devices, such as pen recorders, or in any other recording medium wherein the signals may be displayed in analog form, or may be sent in either analog or digital form to a computer for processing.

My invention is directed to an apparatus and method wherein the electrocardiogram signal (ECG) from the patient is stored in a memory and continually recycled and refreshed and displayed in analog form as a real time display. Preferably, new data appears on one side of a recording medium, such as a tube, and sweeps.

across the medium and is discharged a predetermined time later. All subsequent data follows the same pattern to provide a waveform which moves across the medium. The invention includes means to select an electrocardiogram signal, means to continuously display said signal, means to analyze the signal to determine if it falls within predetermined limits, means to store the signal as an alarm signal, and means to display the alarm signal.

More particularly, my invention is directed to a medical monitor for display of the electrocardiogram. Data from a patient is locally digitized, stored in a shift register, updated, and presented as a swept display. The patient is isolated from the monitor to eliminate fibrillation. A circuit analyzes a waveform corresponding to the ECG signal and determines if it violates certain limits. An alarm system is activated if the signal exceeds the established limits and the alarm condition is represented, visually and/or auditory. All of this is accomplished by a compact self-contained and independent monitor at the patients bedside. In a group of eight (8) monitored patients, if a monitor fails only one patients data is affected. The individual monitors can function without a central Nurses station in the Emergency Ward, Operating Room, Cardiac Catheterization Laboratory, and as a mobile monitor in any part of the hospiml. The invention includes the method of selecting an electrocardiogram signal, displaying continuously said signal for a predetermined time, analyzing said signal to determine if it falls within predetermined limits, storing the electrocardiogram signal as an alarm signal, and displaying said stored alarm signal as desired.

Briefly, certain features of the invention include a persistent or nonfading display, a totally floating input to assure patient isolation from the unit per se, a pat tern recognition device for detection of the electrocardiogram signal to distinguish it from background noise, a digital display of the heartbeat updated on a beat-tobeat basis, and a time delay memory such as a five second auxiliary memory unit to freeze arrythmias or alarm conditions without disturbing the real time displays.

Signals from the patient are fed into an isolated front end wherein the selected electrocardiogram (ECG) signal is amplified and preferably filtered and optically coupled to the main frame of the instrument. The floating front end concept ensures that there is no electrical communication between the patient and the remainder of the system. This provides that in the event the patient is raised to some potential, such as by coming into contact with a source, there is no current path to ground through the patient and this prevents microshock. The front end is protected against defibrillation.

Once the signal has been transferred to the remainder of the system, it follows two paths.

To display the ECG signal, it is filtered to either a diagnostic or monitor band width depending upon the extent of analysis desired. After the signal has been fil tered, it is amplified and then is fed into the display system. The signal passes to an analog-to-digital converter and is sampled a predetermined number of times, such as 200 times a secondfEach time it is sampled a binary number, such as a seven digit binary number, is generated the value of which binary number corresponds to the amplitude of the sample. A plurality of these binary samples are stored in a real time shift register memory. Each time the ECG signal is sampled the binary number generated is entered into the memory displacing the number which represents the sample taken a predetermined sample time earlier. At the same time, the entire memory is being sampled at high speeds. The binary numbers are reconverted into the original signal and rapidly and repeatedly displayed on a cathode ray tube. In essence, the resultant display resembles an electronic analog pen recorder with the paper moving from right to left.

The second path which the signal follow is to a QRS waveform detector and then to a tachometer. The QRS detector itself is a pattern recognition device which detects the duration in time of the first excursion (be it plus or minus) taken in the QRS complex. The duration of this first excursion is approximately -40 milliseconds for both normal and infarcted hearts as nearly as has been determined. By allowing an appropriate window in time for the duration of this excursion, it can be extracted from background noise of similar amplitude.

The tachometer includes a multiple beat rejection circuit which discards bogus beats caused by a patient motion. Such QRS appearing artifact is identified by the indication that it usually occurs in a salvo of rapidly successive peaks. This will not eliminate all artifactual beats but it is clearly an improvement over the present situation in commercially employed equipment. Once the beats are detected, the rate is obtained by inversion of the period between beats. This yields a continually updated rate. The rate is displayed digitally on the front panel of the instrument, and the rate voltage is sent to the alarm section of the unit.

In an alarm section of the unit, there are two comparators to compare the incoming rate voltage with high and low rate limits which are preset from the front panel. With the alarm enabled, violation of either limit will cause actuation of a signal, such as a buzzer, light, or both, each of which preferably correspond to the type of alarm detected; that is, exceedingly fast or slow heartbeat.

Another feature of the invention is an alarm memory in which data, preferably a predetermined time period old, such as five seconds, is continuously fed into the alarm memory. In the event of a violation of an alarm limit which is received on a delayed basis, this memory is sealed off. This captures the event causing the alarm, along with the data preceding and succeeding the alarm event. The information remains locked in this memory until the next alarm occurs unless cancelled or written out. The contents of the alarm memory may at any time be viewed by actuating a switch to display the alarm memory on the cathode ray tube which display preferably appears stationary and below the real time signal.

BREIF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of the total invention;

FIG. 2 is a partially schematic and partially circuit diagram of the flotaing front end;

FIG. 3 is a block diagram of the filter;

FIG. 4 is a circuit diagram of the QRS wave detector;

FIG. 5 is a partially block and partially circuit diagram of the tachometer;

FIG. 6 is an illustration of the waveforms occurring in the tachometer;

FIG. 7 is a circuit diagram of the alarm system;

FIG. 8 is a block diagram of the audio oscillator circuit;

FIG. 9 is a block diagram of the real time memory;

FIG. 10 is a partially circuit and partially block diagram of the timing board employed with the real time memory;

FIG. 11 is a circuit diagram of the interconnection between the real time memory and the alarm memory including the timing for the alarm memory;

FIG. 12 is a block diagram of the alarm memory; FIG. 13 is a circuit diagram of the multiplexer; and FIG. 14 is a schematic illustration of the front panel of the instrument.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The instrument is shown generally in FIG. I wherein a patient is shown at 10 and connected with the three standard-limb leads or Eindhoven Triangle with additional sternal and/or auxiliary leads which communicate with a patient cable I2 which plugs into a patient cable jack [5 on the front panel of the instrument as shown in FIG. 14. The floating front end 14 is optically coupled to a filter-amplifier 26 shown in greater detail in FIG. 3. The signal is filtered and then is directed to a real time memory 200 shown in greater detail in FIG. 9, then to the multiplexer 340 shown in greater detail in FIG. 13, and then to the oscillograph of the cathod ray tube 230. The signal is also sent to the QRS detector 40 shown in FIG. 4, the tachometer 70 shown in FIG. 5, and the digital display 84. The signal from the tachometer is in communication with the alarm system 110 shown in FIG. 7; and if an alarm is actuated, it communicates with the alarm memory system 130 shown in FIG. 12.

FLOATING FRONT END Referring to FIG. 2, the signal from the patient is selected by actuation of the multiple lead selection switch 16 which is also shown in FIG. 14 of the front panel of the instrument and may select any of various wet or dry electrode combinations from among the possible right arm (RA), left arm (LA), left leg (LL), and chest (C) combinations. The switch 16 as shown in FIG. 2 is in 'the 2 position to the RA-LL combination. The lead selection switch may also select a one millivolt calibration signal. Once the switch has selected the combinations of electrodes which will be chosen for display, the signal is amplified and filtered at 18 and optially communicated to the filter-amplifier of FIG. 3 by the optical coupler 24, such as a Monsanto Optical Isolator MCT2.

The power supply 20 for the floating front end is a standard configuration zener regulated power supply. The grounds to the floating front end are identifiedas The supply 20 is coupled to a main power transformer (not shown) of the instrument which is actuated by the OFF-ON switch on the front panel. This communication is by a low capacitance 6O HZ power transformer 21, such as by a Stevens-Arnold isolation coupling No. IT-3408. To prevent a power surge a circuit 26 having neon tubes 28 (NEZH) is employed. When the voltage across them is less than 280 volts, the tubes form an open circuit. If voltage is 280 or greater, then the circuit 26 will act as a short circuit. With the tubes in the open circuit mode, there is no direct electrical communication between the patient and the main power ground of the instrument as shown.

Once the signal has been transferred to the remainder of the system, it will eventually go to the oscillograph of the cathode ray tube and also to the pattern recognition devices, the digital display, and the auxiliary alarm components as required.

FILTER-AMPLIFIER The signal from the front end 14 of FIG. 2 is filtered as shown in FIG. 3. As mentioned in the discussion of FIG. 2, the signal through floating front end is initially filtered at the lower 3 DB point at 0.05 HZ. With the switch 36 on the diagnostic position, the signal is filtered at 29 with the upper 3 DB point at I00 H2. The signal is amplified at gain adjust 30 and then goes to the real time memory of FIG. 9. Accordingly, when the switch 36 is on diagnostic, the signal will be filtered at g the 3DB point with the upper limit at 100 HZ and the lower point at 0.05 HZ. After passing through filter 29, the signal then flows through gain adjust 30 wherein the signal may be amplified from 1 to 20 and then through switch 36.

As shown in FIG. 3, the signals to the QRS detector of FIG. 4 are always between the 1.0 and 40 HZ levels. It should be noted that the filter diagnostic settings correspond with-the specifications of the American Heart Association for analog ECG data to be recorded.

QRS DETECTOR Referring to FIG. 4, the QRS detector 40, a signal as shown enters the wave-shaping network shown at 42. The wave-shaping network is capable of producing two pulses whose waveforms are shown as +d/dt and d/dt. The +d/dt and d/dt pulses are then transmitted to circuit 44 which circuit produces a pulse corresponding in duration to ramp signals with slew rates in excess of +50 V per second or -50 V per second. Thus, the signal from the wave-shaping network 42 goes directly to gate 56 and into matching network 48.

The duration of the first linear rise or fall of the signal is approximately 104O milliseconds for both normal and infarcted hearts as nearly as has been determined. By allowing an appropriate window in time for the duration of this slope, such as from 10 to 40 milliseconds, it can be extracted from background noise of similar amplitude. Thus, a pattern recognition device for detection of the electrocardiographic signal is provided to distinguish it from background noise. When the pulse enters the compare network 48, an input pulse is entered into the network to determine whether or not the pulse received from the wave-shape network has a duration of at least 10 milliseconds. If the pulse received meets the minimum threshold level, 10 milliseconds, then a new pulse is generated by the network 48 which triggers the monostable multivibrator 52 which generates a new pulse of 30 milliseconds. This pulse in turn triggers the next monostable multivibrator 54 to gener ate a pulse of 0.1 milliseconds which is input to gate 56.

If the pulse from the wave-shaping network 42 which was transmitted directly to gate 56 ends prior to the pulse being received from the multivibrator 54, then in fore, if the pulse entering the compare network 48 is.

less than 10 milliseconds, no pulse will be received from the multivibrator 54 by gate 56 and thus gate 56 will not be actuated under any condition. If the pulse as compared is ID milliseconds or more, then the multivibrator will transmit a pulse to gate 56. In order for the gate 56 to trigger a pulse to gate 60, the signal received by gate 56 directly from the pulse-shaping network must end prior to receiving the pulse from the multivibrator; that is, it must be 40 milliseconds or less. Thus, it is seen that if duration of the pulse initially received does not fall within the predetermined window or between 10 to 40 milliseconds, no further signal will be transmitted.

A similar pulse-shaping network, such as 44, to analyze and compare the d/dt waveform has not been shown but functions in the same manner as the circuit 44 and feeds its input to gate 60. If the pulses from network 42 are between the limits set, then they will normally be received in quick succession by gate 60. In any event, even if they vary be a few milliseconds, any pulse received by gate 60 on either input will generate a pulse totrigger the nonretriggerable I00 millisecond delay 62.

Once the nonretriggerable delay has been actuated upon receipt of a pulse from gate 60, a pulse is generated shown as the QRS output to tachometer in FIG. 5.

No new pulses will be generated for 100 milliseconds. This prevents bogus signals from being generated caused by possible overlapping of the signals from the gates.

The pulse is also sent to flasher 63 shown on FIGS. 1 and 12, and to the audio oscillator as will be descirbed in more detail in the description of FIG. 8. The flasher systole 63 is simply a light emitting diode, such as a Monsanto MVSO, actuated upon receipt of a signal from the multivibrator 62. Any suitable visual indicator may be employed.

TACHOMETER Referring to FIG. 5, the pulses from the QRS detector of FIG. 4 enter the tachometer; specifically, the

pulse enters the OR gate 71 then to the sample and hold circuit 76 and the delay circuit 72, which triggers the ramp generator 74.

The pulse shapes are shown in FIG. 6 divided into three sections, I20 beats per minute (BPM), 6O BPM, and 20 RPM. Also shown in the 20 BPM section is the comparator output. Sample command from the gate 71 is shown as line a, the 100 microsecond delay pulse is shown as line b, the signal from the ramp generator is shown as line 0, the sample and hold circuit output as line d, the divider output as line 2, and smoothing circuit output as linef. As indicated, the sample and hold circuit selects that value of the slope from ramp generator 74 and provides and holds the waveform'or voltage proportional to the period between pulses as shown in line 6d. Each time a pulse is received from the QRS detector, the ramp generator 74 is reset to zero by the I microsecond delay circuit 72. If no pulse is received from the QRS detector within the time period corresponding to the time'it takes the ramp generator to reach a threshold value of 2.5 volts as determined by the comparator 74, the ramp generator will provide a signal to gate 71 to trigger a pulse corresponding in time to the 2.5 volt value, the sample and hold circuit thus generating a new waveform. The preset 2.5 volt value of the comparator corresponds to a heart rate of 20 beats/min. or approximately 3 seconds between beats. This is also shown in FIG. 6.

The pulse from the sample and hold circuit is received by the analog divider 78, wherein a one volt input at b provides the numerator for the division and the sample and hold output provides the denominator. The signal from the analog divider 78 is a voltage proportional to the frequency of the pulses. The output of the analog divider ranges from O V for 0 BPM to V for 300 BPM. This signal is received by an amplifier and offset circuit 79 wherein the 0 to 300 BPM voltage range is changed to volts. From amplifier 79 the signal enters smoothing circuit 80 which is designed to prevent the transmission of any further signals to the analog to BCD converter unless they exceed certain limits. As shown, a short term change in BPM of ill or less, (i0.7 V) will not be reflected on the digital display 84. Thus, the smoothing circuit 80 prevents flicker. The one millisecond delay circuit 83 prevents entry of any signals into the converter 82 until the other components of this circuit have stabilized, particularly the sample and hold and ramp generator circuits. The converter 82 includes a gate which will transmit information to the display when signals are received from both the delay circuit 83 and the smoothing circuit 80.

ALARM Referring now to FIG. 7, the alarm circuit is shown generally at and receives a signal from the tachometer described in FIG. 5 which signal corresponds to the rate voltage sent to the digital display 84. Comparators 112 and 114 are preset through variable resistors 116 and 118 to determine the high and low limits ofthe rate voltage which should not be violated, such as a high limit of approximately 2 volts corresponding to 120 BPM and a low limit of approximately 0.6 volts corresponding to 40 BPM. The incoming signal from the tachometer is analyzed in the comparators. If neither condition is violated, no alarm signal is generated by gate 119. Violation of either limit will provide a signal and as shown will (a) actuate the front panel lamp, such as a MV-SO, either tachycardia 120 or the bradycardia 122 depending upon whether the upper or lower limit has been violated; (b) provide an audio signal, high or low, transmitted to the audio oscillator of FIG. 8; (c) transmit a further signal to the audio oscillator of FIG. 8; and (d) transmit a signal to the alarm memory of FIG. 12.

Two switches are shown, an alarm set-reset switch 128 and an alarm response switch 124, which includes a five second delay latch circuit 126. When in the normal position, switch 124 allows the signal to be transmitted instantaneously to the audio oscillator and the alarm memory. When actuated, the alarm response switch 124 will delay the alarm signal for five seconds by engaging the latch circuit 126.

Since it is possible for the unit to receive abberrant beats, this capability of selecting a five second delay to the alarm system is provided. If the alarm condition persists for five seconds, then the instrument will generate an alarm, but not before. The five second delay circuit may then be reset after the alarm condition has been checked through the switch 128 which also cancels the signal to the audio oscillator of FIG. 8. In instantaneous mode the alarm is reset automatically when the alarm condition ceases.

AUDIO OSCILLATOR Referring to FIG. 8, a block diagram of the audio 05- cillator is shown wherein a QRS detector input line is shown receiving the signals from FIG. 4 which flow directly to an analog switch 91. From the switch they go to the mixer 92 where they are amplified through the speaker 95. The signals from the QRS detector provide the actual impetus for the sound corresponding to the heartbeat. A voltage controlled oscillator (VCO) systole sound is shown at 97 and receives a signal from the smoothing circuit of the tachometer of FIG. 5. This deterrnines the frequency or the pitch at which the signal received from the QRS detector output will be heard. The alarm circuit pulses are received from low alarm, high alarm, and from the gate 119. A signal from high alarm will be transmitted to gate 94b. If a signal if received from gate 119 of FIG. 7, then the gate will actuate analog switch 96b which receives the characteristic sound from the phase shift oscillator 92b. The signal goes to the mixer 93 and then to the speaker 95 also shown on the front panel. The mixer is of the type which is'adapted to receive and pass all signals simultaneously, as is well known in the art. It serves no other function than to allow the various signals to pass through a common point to the speaker 95. The VCO 97 may be adjusted to vary the volume of the systole sound to give an indication of the heartbeat, and the phase shift oscillators may also be adjusted to change the level of sound of the high and low alarms. These are shown on the front panel.

REAL TIME MEMORY Referring to FIG. 9, the real time memory is shown generally at 200. The analog signal from FIG. 3 is receivcd by the analog-to-digital converter where the analog is sampled and digitized each time a start pulse occurs, as will be explained later. As shown, this is 200 times per second. the a/d converter is of a standard downcounter design. The output of the a/d conversion is a 7 bit binary signal. Shift registers 204a-g, 2061-2. are each 512 bits long, and each have a binary input and a two phase clock input together with memory cells as with all commercially available shift registers, such as National Semiconductor MM50I6. The clock input of the shift registers receives a continuous series of pulses at the rate of 204.8 KHZ/sec. from the clock 208. The digital signal appearing at the input of the registers will appear at the output of the registers after one-two-hundredth seconds or 1024 clock times. As shown, the output of the shift registers, for example shift registers 204a and 206! 204g and 2062, are wired back to the inputs and data is continually passed back through the registers or recirculated. Switches SW-I through SW-7 with continual clock pulses to the 1024 bit registers from the clock operate with the following cycles synchronized to the clock. For 1024 clock times, recirculation takes place, then for 1 clock time new data from the a/d converter 202 is entered into the register and the register and the cycle repeats. The result of this operation is that the registers are continually being updated with new information at the rate of 200 pieces of data per second. The output of the register is fed to a continuous d/a converter which produces an analog voltage from the 7bit register 210.

The two phase clock 208, shown in greater detail in FIG. 10, provides two modes of operation during a clock time. The modes are respectively to read data and then shift data. On the read mode of the first clock pulse the data from the a/d converter is read or examined, and on the shift mode of the first clock pulse the data is entered into the first position of the register 204a. On the second clock time, the read pulse, new data is entered into the first position of the shift register while the old data shifts to the second position of the shift register. This continues on until completion of the I024 clock time. On the 1025 clock time the original data is reentered into position 1. At the end of the 1025 time, the switch SW-l is actuated to allow entry of new data. At the end of 1026 pulses or the first pulse of the second cycle, the original data is in position 2 and the new data is now in position I.

Stated another way, referring specifically to registers 204a and 2061, which in series make up a 1024 bit register, apiece of data entering register 204a in the first position at time 0 will at time 1023 be in the 1024 position of shift register 2061. During clock time 1025 this bit of information will have been recirculated and entered shift register 204a in the second position of the 1024 positions available. At clock time 1025, switch SW-l is actuated and new data is introduced into the first position of shift register 204a with the old data now in the second position of shift register 204a. With the 1025 clock times later the data in positions 1 and 2 will have recirculated through shift registers 204a and 206! and will have entered the second and third positions of shift register 204a. At clock time 2050 switch SW-1 is actuated and new data is entered into the first position of shift register 2040. From the above values it is seen that in approximately five seconds the first bit of information entered into the first position of register 204a will have recirculated approximately l,024 times and be in the lO24th position of shift register 206:. The same sequence is followed for shift registers 204hg and 20614-2.

Referring to FIG. I0, the two phase clock is shown generally at 208. The circuit generates complementary pulses, d: in and (1) out. These voltages are alternately emitted at +5 (and when not at a voltage of +5, they are at a voltage of -12). As described above, these pulses are transmitted to the shift registers and correspond to the read pulse and shift pulse for each clock time. When the shift pulse goes to the shift registers, it also enters the level shifter shown at 240. This level shifter allows the 5 volt output to alternate between +5 and 0 volts. The output from the level shifter 240 goes to the a/d converter shown in FIG. 9, to the divide by 1025 circuit or register 242, and to gate 306!) of FIG. 11. This circuit 242 is comprised of three divide by 16 counters 480a, b, and 0. During clock time 1, the register reads zero. During clock time 2, the register reads one. Pgring clock time 3 the register reads two, etc., until during clock time 1025, the register reifi s l 024 At the end of clock time 1025, the register reverts to the zero state. When the register reverts to zero, a signal is gated to pulse generator 244 which which actuates switches SW-l to SW-7 to allow for the entry of new data into the shift registers. As shown the pulse generator has two outputs A and B. During clock times 1-1025 the output from A allows recirculation of data and the output from B inhibits entry of new data. When the signal is gated to the pulse generator 244, the outputs of A and B are reversed.

Referring to FIG. 11, the switching and command mechanism for the real time memory is shown in FIG. 11 for shift registers 204a and 2061, it being understood that similar command and switching mechanisms are duplicated for the remaining shift registers. The switch: ing and command and the timing forthe alarm memory are also shown. Gates 300a and 30% are synchronized with the clock times and upon completion the I025 clock time, new data is entered into the first position of the 2040 register and at the same time this new data is transmitted to the digital-to-analog converter 210 of FIG. 9. This condition occurs when the input to the 300a gate is 0 and the input to the 30% gate is l These inputs are 0 from A and 1 from B of the pulse generator 244. On the 1024 clock times, the input to the gate 300a is 1 and the input to the gate 30% is O. This prevents the transmission of new data to the registers and allows recirculation of the present data to the shift registers. When the new data is accepted at the end of the 1025 clock times, the old data leaving the 1024 position of register 206:, goes to inverter 310, then to gate 302b and to D/A 210.

The alarm memory 320 comprises the same number of shift registers and of the same characteristics as of the real time memory 200. Thus, the data which is five seconds old is entered into the alarm memory 320. This five second old data is recycled in the same manner as 

1. A device for analysis and display of electrocardiogram (ECG) signals which comprises: a. means to provide an ECG signal; b. a real time memory which includes:
 1. means to receive the ECG signal and convert the signal to digitized form;
 2. means to store the digitized signal for a first predetermined time which corresponds to the time required for the digitized signal to enter, be recycled, and discarded; c. means in communication with the real time memory to display continuously the digitized signal in the real time memory in analoG form on a medium; d. means to analyze the ECG signal to determine if the signal falls within at least one predetermined limit, which limit corresponds to a rate value which describes an alarm condition and means to provide an alarm signal of the limit is violated; e. an alarm memory which includes:
 1. means to receive the ECG signal in digitized form;
 2. means to store the digitized signal for a second predetermined time, which corresponds to the time required for the digitized signal to enter, be recycled, and discarded from the alarm memory; and
 3. means responsive to the presence of the alarm signal to lock in place and prevent the discard of the digitized signal stored in the alarm memory; and f. means in communication with the alarm memory to display in analog form the digitized signal locked in the alarm memory on a medium.
 2. means to store the digitized signal for a second predetermined time, which corresponds to the time required for the digitized signal to enter, be recycled, and discarded from the alarm memory; and
 2. means to store the digitized signal for a first predetermined time which corresponds to the time required for the digitized signal to enter, be recycled, and discarded; c. means in communication with the real time memory to display continuously the digitized signal in the real time memory in analoG form on a medium; d. means to analyze the ECG signal to determine if the signal falls within at least one predetermined limit, which limit corresponds to a rate value which describes an alarm condition and means to provide an alarm signal of the limit is violated; e. an alarm memory which includes:
 2. The device of claim 1, which includes means to distinguish the ECG signal from background noise, whereby only those ECG signals falling within a defined range are selected for analysis.
 2. means to store the digitized signals therein for a second predetermined time which corresponds to the time required for the digitized signal to enter, be recycled, and discarded; and
 2. means to convert the distinguished ECG signal to a wave form which has a rate voltage inversely proPortional to the duration between successively generated ECG signals; and
 2. means to store the digitized signal for a first predetermined time, which corresponds to the time required for the digitized signal to enter, be recycled, and discarded; c. means to analyze the ECG signal to determine if the signal falls within predetermined upper and lower limits, which means includes:
 3. means to provide an alarm signal when either the upper or lower limit is violated; d. means to transfer the digitized ECG signals from the real time memory to an alarm memory, which alarm memory includes;
 3. means responsive to the presence of the alarm signal to lock in position and prevent the discard of the digitized signal in the alarm memory; and e. means in communication with the real time memory and the alarm memory to display continuously the digitized signal in the real time memory in analog form and to display the digitized signal in the alarm memory in analog form.
 3. means responsive to the presence of the alarm signal to lock in place and prevent the discard of the digitized signal stored in the alarm memory; and f. means in communication with the alarm memory to display in analog form the digitized signal locked in the alarm memory on a medium.
 3. The device of claim 2, wherein the means to distinguish the ECG signal from background noise includes a wave-shaping network to convert the signal to a pulsed signal and a matching network to determine if the duration of the pulsed signal is within the defined range.
 4. The device of claim 3, which includes means to establish the defined range between 10-40 milliseconds.
 5. The device of claim 1, which includes means to convert the ECG signal to a wave form which has a rate voltage inversely proportional to the duration between successively generated ECG signals.
 6. The device of claim 5, which includes means to display the value inversely proportional to the duration between pulses in digital form.
 7. The device of claim 1, which includes means to determine if the ECG signal falls within upper and lower limits, which limits correspond to rate values which describe alarm conditions whereby an alarm signal is generated when either limit is violated.
 8. The device of claim 7, which includes means to establish the upper and lower limits as voltage limits.
 9. The device of claim 7, which includes means to delay the transmission of the alarm signal to the alarm memory.
 10. The device of claim 1, which includes means to transfer the digitized signals from the real time memory to the alarm memory.
 11. The device of claim 1, which includes means to transfer the digitized signals discarded from the real time memory to the alarm memory.
 12. The device of claim 1, which includes means to delay the locking of the digitized signal in the alarm memory subsequent to the receipt of the alarm signal whereby the digitized signal corresponding to the ECG signal which ECG signal violated the limit and generated the alarm signal is locked in the alarm memory in a position intermediate its entry and discard from the alarm memory.
 13. The device of claim 1, which includes the means to display the information locked in the alarm memory on the same medium that the digitized signal in the real time memory is displayed.
 14. The device of claim 13, wherein the medium is a cathode ray tube.
 15. A device for the analysis and display of electrocardiogram (ECG) signals, which comprises: a. means to provide an ECG signal; b. a real time memory which includes;
 16. The device of claim 15, wherein the means to distinguish the ECG signal from background noise includes a wave-shaping network to convert the signal to a pulsed signal and a matching network to determine if the pulsed signal is within a defined range.
 17. The device of claim 15, which includes means to delay the transmission of the alarm signal to the alarm memory.
 18. The device of claim 15, which includes means to transfer the digitized signals from the real time memory to the alarm memory when the digitized signals are discarded from the real time memory.
 19. The device of claim 15, wherein the alarm memory includes means to delay the locking of the signals in the alarm memory subsequent to the receipt of the alarm signal whereby the digitized signal corresponding to the ECG signal which ECG signal violated the limit and generated the alarm signal is locked in the alarm memory in a position intermediate its entry and discard from the alarm memory.
 20. The device of claim 19, wherein the means to delay the locking of the information in the alarm memory includes at least one latch circuit.
 21. The device of claim 15, which includes means to display the digitized signal in the alarm memory at any time subsequent to the locking of the signals in the memory.
 22. The device of claim 15, which includes means to display on the same medium the digitized signal in the real time memory and the digitized signal in the alarm memory, the signals spaced apart from one another along a vertical axis.
 23. The device of claim 15, which includes means to display digitally the rate voltage.
 24. The device of claim 15, which includes means to display audibly the analyzed ECG signals.
 25. A method for the analysis and display of electrocardiogram (ECG) signals, which includes: a. providing an ECG signal; b. converting said ECG signal to digitized form and storing the same in a real time memory for a first predetermined time which corresponds to the time required for the digitized signal to enter, be recycled, and discarded; c. displaying continuously in analog form the digitized signal in the real time memory on a medium; d. analyzing the ECG signal to determine if the signal falls within predetermined limits, which limits correspond to rate values which describe alarm conditions; e. providing an alarm signal when either of the limits is violated; f. receiving and storing the ECG signals in digitized form in an alarm memory for a predetermined second time which corresponds to the time required for the signal to enter, be recycled, and discarded; g. locking and preventing the discard of the digitized signal in the alarm memory in response to the alarm signal of step (e); and h. displaying in analog form the digitized signal locked in the alarm memory.
 26. The method of claim 25, which includes distinguishing the ECG signal from background noise.
 27. The method of claim 26, which includes converting the distinguished ECG signal to a wavE form, which has a rate voltage inversely proportional to the duration between successively generated ECG signals.
 28. The method of claim 25, which includes displaying the rate voltage in digital form.
 29. The method of claim 25, which includes transferring the digitized signal in the real time memory to the alarm memory.
 30. The method of claim 29, which includes transferring the digitized signal to the alarm memory upon discharge of the signal from the real time memory.
 31. The method of claim 25, which includes delaying the locking of the digitized signal in the alarm memory subsequent to the receipt of the alarm signal whereby the digitized signal corresponding to the ECG signal which ECG signal violated the limit and generated the alarm signal is locked in the alarm memory in a position intermediate its entry and discard from the alarm memory.
 32. The method of claim 25, which includes displaying the digitized signal in the real time memory and the digitized signal in the alarm memory, in analog form on the same medium, said signals spaced apart from one another along a vertical axis.
 33. The method of claim 32, which includes displaying the digitized signals in the alarm memory at a time subsequent to the locking of the signals in the alarm memory. 